JLab Update Rongli Geng April 30, th LCC ILC Cavity Group Meeting

High Gradient SRF Themes Understand and reduce field emission –Cavity vertical testing at Epk 100 MV/m –Gradient and Q0 degradation due to field emission from vertical testing to operation in cryomoudle CEBAF upgrade cavity experiences Improve efficiency at high and very high gradient –New shape – higher R/Q and lower Hpk/Eacc –Large-grain material –Frozen-in flux (and response to thermal cycling)

JLab Status: Field Emission Instrumentation Installation X-ray sensors (Hamamatsu S ) at all cavities in full FEL cryomodule –Compare field emission data at VTA testing with cryomodule testing –Establish correlation between FE induced X-ray and FE induced Q0 loss and dark current at end of cryomodule –Cryomoudle in test cave. Test to be started soon. F100 cryomodule cavity string being assembled and to be tested One X-ray sensor for each cavity near beam tube flange

JLab Status: High Q0 at 45 MV/m Two single-cell large-grain niobium cavities under processing and testing for high Q0 at ultra high gradient regime of > 45 MV/m –New LSF shape 1-cell large-grain cavities (Two each) In collaboration with Peking University, Ningxia Large grain material. Processing procedure: BCP + 800CX2hr + BCP + 120C bake. Test data later slide. One new single-cell large-grain niobium cavity under processing and testing –Cavity PJ1-2 In collaboration with Peking University and OTIC, Ningxia large-grain Nb material and fabrication. CEBAF upgrade cavity Low-loss shape, 1.5 GHz. Processing procedure: BCP60um+800Cx2hr+BCP60um+HPR+120Cx48hr. Max. Eacc 34 MV/m with Q0=1.6E10 at 2K, limited by quench, no FE. Max. Eacc 34 MV/m with Q0=2.5E10 at 1.8K, limited by quench, no FE. Next is EP and re-test. Test data later slide.

Max. Eacc=38 MV/m with Q0=2E10, no X-ray, quench limit LSF1-2 Cold Test Result